Satellite communication system



July 4 .1944. fr; A. MARSHALL SATELLITE COMMUICATION SYSTEM.

Filed Sept. 19, 1942 3 Sheets-Sheet 1 l rhs RLY lNVEA/TOR by fIAMARSHAQ.

ATTORNEY July 4, 1944- T. A. MARSHALL 2,353,055

` SATELLITE COMMUNICATION SYSTEM Filed sept. 19. 1942 s sheets-sheet 4FOL A RIZED PQL AR/ZED ./Nl/ENTOR A7. MARSHALL BY I A 7- TURA/EY July 41944- T. A. MARSHALL 2,353,055

' SATELLITE COMMUNICATION SISTEM Filed epi. 19, 1942 3 sneetssheet s Ials /N VEN TOR 77 A. MARSHALL JWM' Patented July 4, 1944 SATELLITECOMMUNICATION SYSTEM Tola A..Mar`shall, Floral-Parmi N. Y., assignorito:

Bell- Telephone Lab oratories, Incorporated,

New York, N. Y., a corporation of New York l Application september 19,1942, serial No. 458,979'

16 Claims.

This invention. relates to communication systems and more particularly,tol teletypewriter eX- change systems wherein satellite arrangementsprovide for. a plurality of subscriber stations being connected throughan automatically operated line concentrating unit switching center, to acentral oi'lce.

. In. order to assist in understanding the invention. vit is desirableto briefly describe the present arrangement of the teletypewriterexchange central oice equipment and the method of operating andmaintaining the trunk circuits extending to other central oflices andthe terminating equipment at opposite ends' of each trunk.

.The operating and maintenance personnel may be divided roughly vintotwogroups:

A. A traic group which comprisesthe operators for establishingconnections and the supervisory forcerouting and supervising thetraffic; and

B. A plant group Whose duty it is tomaintain the circuits in properoperating condition, locate the causes of trouble when reported by thetraffic group, and to clear the varioustroubles after the causes havebeen ascertained,

.The Various trunkv lines are multipled before several operators at,positions of the operator.

switchboard to permit the operators to estab-v lishconnections. Ifanoperator nds a'particu-- lar line or trunk in trouble, she reports thisfact.

to a. traffic control bureau which is usually located in some other partof the building and has l no direct access tothe `line ,or trunk. introuble. Itis desirable. that thetrafc control bureau verify the factthat the. trouble exists before nol tifying the plant people vto clearit and in order to do this, the traic controlr bureau orders a.

trouble operator (whois located at oneof. the

positions of the toll switchboard)y to extend the line or trunk, introuble, to ,the traffic control b ureau.r The troublehaving beenveriiied, it is reported to a troubleclerk in the plant department whomakes out a ticket and delivers it to the attendant at'a test boardwhose duty it isto determine. the cause of( the trouble. The test boardis lso arrangedjthat each attendant thereat has access toa certain groupoflines,and/or trunks andthe lines or trunks arenot multipled to otherpositions at the testboard.Y If at the time the trouble is reported .tothetrouble clerk theattendant at the. test `board should be busy testinganother linear trunk, he would'not be able to take up the new troubleimmediatel?,k and vlienc'e, the

necessity forL making outfaticket and delivering it 'to the attendant.As son as the te'st board attendant has determined trouble heinstructs'theproper equipment man who has charge of the. partic 1,1la'1.eluipinrit` which is in trouble, to clear it. 'After the trouble viscleared the equipment man notifies the test board attendant, who again`tests.to ,determine that the vlinel or trunk and apparatus associatedtherewithare inpropercondition; ,whereupon he notifies the trarnecontrol bureau that the .une or trunk isagain ready for service.

When the traic control bureauorlginally vascertained that'thetrouble'existed,. the trouble operator at e e the toll switchboardwasordered to render the The applicant has foiindvitv` desirable to,v,sima plify'th'e operationof testing each trunkextending from a centraloflice to a line concentrating unit switching center end each of thesubscriber lines connected eitherdirectly 'tito the switching,

center erover any one of lthese trunks.

'An pbject ofi the myentoin is to test attnecrf tial oice theoioeratiinalv eiectiveness of each of the circuits extending between thecentral oice and theline concentrating unit switching center, and eachof thesubscribers lines connected directly to the switching center,

According to the present invention a testing position, in addition to aplurality of theusual operator positions, is provided at the operatorswitchboard at the central cnice.I At the testing position each of thetrunks incoming lfrorn the line concentrating unit switchingmcenter isterminated, inv multiple appearance, at a jack. Also terminating at Athetesting positionoi'the operator Vswitchboard in'addition to a pluralityof cord circuits, is another cord'circuit connected to a testing trunkcircuit whicheitends Yto a test board located in a part of the buildingother than that wherein the operator switchboardis located. Therefore, atest board attendant may, at any desired time or'at regular intervalslrequest. over an order Wire the operatorat the testingA posif tion ofthe operator switchboard to .connect the testing trunk plugnto thejackof any parti cular trunk extending to the line concentrating unit.

vswitching center, s o that the .tes t a bpard,attendm ant may originatea call to another 'test board the 'cause' of4 the troubled circuit busyandthe busy. conditionexisted during theperiod of making out theticket,'testing and clearing the trouble.

attendant at the line concentrating unit switching center, or to any ofthe subscribers stations directly connected to the switching center orto any other subscribers station directly connected to the centraloffice, and supervises such connections in the same manner as anoperator at an operator switchboard.

A feature of the present invention is the provision for makingranover-all test on any one of the trunks extending to the line circuitswitching center, with the supervisory signals coming from a subscriberstation or attendant teletypewriter trunk circuit at the lineconcentrating unit switching center, or for making the tests locallywith supervisory signals simulated at the jack associated with theparticular line or trunk in the test board at the central oce.

Another feature is the direct means for testing trunks extending to theline concentrating unit switching center by requesting the operator atthe test position of the operator switchboard to connect the testingtrunk circuit to any one of the trunks through its multiple jack whichappears at the test position.

Another feature is the provision of a high resistance sleeve conductorinthe testing trunk cord circuit which, when connected to a trunk,loperates a guard lamp at the test board but does not operate a sleeverelay in the particular trunk selected.

Another feature is the provision of a makebusy jack in the testing trunkcircuit arranged to be patched with a cord circuit to the makebusy jackof the selected trunk wherebya busy lamp and an answer lamp are arrangedto light over the sleeve and the tip conductors, respectively, of thetesting trunk cord circuit, the answering lamp lighting one-half secondlater than the busy lamp. i

Another feature is the provision for extinguishing the answer lamp andthe busy lamp at the test board successively when the call is abandonedbefore it is answered. Resumption ofthe call within four secondsrelights the answer lamp. Resumption later than four seconds is like anew call. l i fr! Another feature is the provision for answering a callat the test board by restoring a locklng key to normal whereby theabove-mentioned high resistance of the sleeve conductor of the testingtrunk cord is reduced, to operate the sleeve relay of the selected trunkand circuits are closed to cause the guard lamp at the test board tolight and extinguish the answer lamp.

Another feature is the provision when a recall signal is received at thetest board, to furnish interrupted ground potential to a circuit forflashing a supervisory lamp. The lamp is extinguished by the momentaryoperation of a nonlocking restore key.

Another feature is the provision for originating a call at the testboard after the selected trunk is made busy. by operating'the lockingkey connecting the testing trunk cord to the selected trunk and thenrestoring the locking key.V A supervisory lamp at the test board willlight steadily after the key is released.

Another feature is the provision of a relay arranged to release whenground potential is removed from the ring conductor of the trunk.indicating that the line concentrating unit is ready to receive calldirecting pulses. The relay, polrli releasing, causes the supervisorylampto Another feature isthe provision of applying 75 a steady groundpotential to the ring conductor of the testing trunk cord circuit whenthe connection of a subscribers line, in response to the call directingpulses, is completed at the line concentrating unit for causing thesupervisory lamp to change from a flashing light condition to a steadylight condition.

Another feature is the provision of applying ringing current totheselected trunk by operating a key at the test board which current istransmitted to the line concentrating unit as 20-cycle dot signals.

Another feature is the provision of changing the supervisory lamp from asteady light conditionto a flashing light condition when the call to orthrough 'the line concentrating unit is answered, -A momentary operationof the restore key at the test board extinguishes the supervisory lamp.

Another feature is the provision for testing the functioning of theselected trunk circuit on a disconnect by the operator before asubscriber disconnects, by operating a locking key at the test boardwhich opens the sleeve circuit of the testing trunk cord causing thetrunk sleeve relay to release. 'Ihe release of the trunk sleeve relaycauses the answer lamp at the test board to light If the subscriberdisconnects before the locking key is restored the answer vlamp isextinguished and in five seconds is followed by the extinguishing of thebusy lamp. Y

Another feature isthe provision of means for testing the functioning ofvthe selected trunk circuit when the party at the opposite end of thetrunk disconnects, whereby ground is applied to the ring conductor ofthe testing trunk cord to cause the supervisory lamp at the test boardto light.

Another feature is the provision of means for testing the functioning ofthe selected trunk circuit when the operator disconnects after the partyat the opposite end of the trunk circuit disconnects. This condition issimulated by operating the locking key to open the sleeve circuit of thetesting trunk cord. The busy lamp at the test board is extinguished oneand one-half seconds after the operation of the key. The guard lamp atthe test board is maintained lighted and the trunk sleeve relay remainsreleased removing the condition which has kept the busy lamp lighted.

'I'he drawings consist of three sheets. The first sheet contains Figs. 1and 4, the second sheet Fig. 2, and the third sheet Fig. 3.

Fig. 1 is a diagrammatic showing of a subscriber station connectedthrough a line concentrating unit switching center to a central office.Other subscriber stations, not shown, may likewise be connected to theline concentrating unit switching center. The equivalent of a subscriberloop is shown connected to a jack at the attendants test board at theline concentrating unit switchingcenter for the purpose of testing anyone of the` trunks extending between the central office and the lineconcentrating unit switching center. The subscriber station may besimilar to that shown in Fig. 3 of the copending application of C. W.Lucek,l Serial No. 431,854, filed February 21, 1942. Likewise, thesubscriber line terminating circuit, the link circuit, the sequencecircuit, the trunk circuit, the director circuit, alltrunks-busycircuit,.and the miscellaneous alarm circuit provided at the lineconcentrating unit switching center, represented by rectangle H4, may besimilar to the corresponding circuits nating equipment shown in Fig. V2.Test plug 20|` ofv the testing trunk is inserted in'jack 203 which is amultiple appearance ofl the selected trunk at the test position of theoperator switchboard. The test board attendants teletypewriter isinserted by means of its attached cord landY plug, into test jack 302.The automatic signaling.

trunk key SIS is used and its operation is hereinafter described. Thetest board attendants teletypewriter may also be inserted in loopingjack 303 for testing outgoing trunks'or in jack 3I2 for callingtheoperator at the test position of the operator switchboard, Y

When the trunk circuit shown in Figs. 1 and 2 is in the idle condition,both the inward andthe outward paths are in spacing condition. No relaysor vacuum tubes are energized except receive supervisory relayl 2RSWhichis normally held in its spacing position by the'spacing 'conditionof the outward path which extends through the upper winding of therelay. Relay 2RS will maintain condenser 224 discharged while thek trunkis in an idle condition.

Trunk busy atoperator switchboard If the automatic signaling trunkcircuit is Abusy at the operator switchboard appearance while themake-busy jack 3I3 is patched to the makebusy jack 3|5 in the trunkcircuit, busy lamp 3H will be lighted over a circuit traceable fromgrounded battery 225, say of 48 volts, resistance 226, say of 284 ohms,contact and middle lower armature of trunk-busy relay 2BY, sleeve con`ductors of jack 3|5, cord 3|4 and jack 3|3, through the lamp 3H toground. .If a calling signal incoming over outward path R is awaitinganswer at the operator switchboard, as indicated by the lighting ofcall, or line, lamp 205, busy lamp 3| 'l will light because busy relay2BY is operated, and answer lamp 3H will light over the circuittraceable from grounded battery 221, say of 48 volts, resistance 228,say of 284 ohms, outer lower armature and contact of lamp relay 2L, tipconductors of jack 3|5, cord circuit 3|4 and jack 3|3, through the lamp3| I to ground.

In response to a callingV signal incoming'over outward path R relay 2RSfollows all pulses of the calling signal. During the idle condition ofthe trunk relay 2RS will keep condenser 224 discharged. Marking pulsespermit condenser 224 to charge and will energize the filament circuit ofvacuum tubes 2|3 to 2|'|. When a marking pulse in excess of one-halfsecond is received as the result of a call, condenser 224 will chargesuiliciently to cause tube 2 I6 to draw plate current and operate relay2C which, in turn, operates relay 2CT. Relay 2CT, upon operating, willopen the spacing contact circuit of relay 2RS so that tube 2|6 willremain conductive. Relay 2CT, upon operating, will also condition relay2R so as to follow the signal pulses from the outward path, and willoperate relay 2TR. Relay 2'I'R, upon operating, will lock itself in anoperated position and operate relay 2-ON. Relay 2-ON, upon operating,applies power to the repeater relays 2R, 2S and 2SS and operates-busyrelay 2BY. Relay 2BY, upon operating, lights bfusy lamp 202, energizesthe filament circuit of the vacuum tubes independently of the markingcontact of relay 2RS and applies a busy potential` to the sleeve of jack203. Meanwhile, the tube illaments being energized, tube 2 |5`becomesconductive and prior to theoperation of relay 2-ON operates relay Awhich, in turn, operates relay 2AI so that the 20-cycle current fromsource 233 will be transmitted over. the inward path T when armature ofrelay 2EI, and transfers condenser 229 from ground to a high resistancecharging path including resistances 234 and' 209 and grounded positivebattery 208. When condenser 229 has charged for a period of one-halfsecond tube 2|4 becomes conductive and relay 2E oper-Y ates to operate,in turn, relay 2EI. Relay 2E|, upon operating, will close the operatingpathof relay 2L, which, upon operating, will light call, orline, lamp205 and operate night alarm 235. 'I'he circuit for operating relay 2L istraceable from grounded battery on the winding of relay 2L, conductor230, middle upper armature and contact of relay 2EI, contact and innerupper armature of relay 2CT, contact and lower arma-v ture of relay 2A|to ground at the innermost lower armature and back contact of trunksleeve relay 2SL.

If the trunk shown inFig. 2 is idle at the time jacks 3|3 and 3|5 arepatched together, neither the busy lamp 3| 1 nor answer lamp 3| I willlight. However, the trunk may be made busy by the attendant at the testboard by inserting the plug of patching cord 3|4 in make-busy jack 3| 5to connect ground to the ning spring of the jack and thereby close thecircuit extending over. conductor 342, through the winding of relay 2TS,to grounded battery and relay 2TS operates to connect source 23| ofalternating current to a circuit extending over the outer lower armatureand contact of relay 2TS to the trunk-busy lamp 202 which lightsindicating that the trunk is busy.

Connecting the testing trunk plug 201 at the test position of theoperator switchboard If the trunk is found to be idle, plug 20| will beconnected to the multiple appearance at the testing position of theoperator switchboard after rst operating automatic signaling trunk testkey 3|6. Operation of key 3|6 to its open condition provides a highresistance circuit extending from grounded battery, through a highresistance winding, say 20,000 ohms, of relay 3T, contact and lowerarmature of relay 3U, conductors 353 and 323, sleeve conductors of plug20| and jack 203,` through the winding of trunk sleeve relay 2-SL toground, and relay 3T operates but relayv 2SL does not operate at thistime. Relay 3T,

upon operating, closes at its armature and con# tact a circuit traceablefrom grounded battery g; 3|9, say of 48 volts, conductors 343 and 344,contact and armature of relay 3T, conductor 345, through guard lamp 30|,to ground and guard lamp 30| lights to indicate that testing trunk cord206 is connected to a main trunk.

Incoming call An incoming call from the distant'switching center H4,which originated at either the center itself or one of the subscriberstations connected f'r thereto, will cause busy lamp 3|? to light overthe sleeve circuit as hereinbefore described and answer lamp 3|| tolight over the tip circuit of jack 3|3, also as hereinbefore described.The answer lamp 3| I lights one-half second later than the busy lamp 3H.

answer lamp 3H will be extinguished and be followed by the extinction ofbusy lamp 3|1. Ref

"Disconnection while subscriber station is still connected forcommunication Atest for the functioning of the automatic sig- 'nalingtrunk-circuit shown in Fig. 2 on a dis- 'connect vby the operator beforethe subscriber disconnects may be made vby operating the autog, -maticsignaling trunk key 3l which, when op- Yerated, opens the sleeveconductor 323 ofthe `testing cord 26. Relays 3SI and 3U release.V

'Relay 3U, upon releasing-closes a circuit extending through the highresistance winding of relay 3T to grounded battery. During the openinterval of the sleeve conductor 323 of cord 206 before relay 3T isconnected, the trunk-sleeve relay ESL is given an opportunity to releaseonthe ybusy condition being maintained by the presence of the connectionto the make-busy jack3l5 oi the trunk circuit. 'I'he release of thesleeve relay in the trunk circuit causes relay 2L to operate, which,upon operating, causes the lighting of answering lamp 3II. connectsbefore the automatic signaling trunk key 343 is restored, the answerlamp 3H is eX- tinguished and in ve seconds is vfollowed by theextinction of the busy 'lamp 3H. v

Subscriber disconnects 'first Disconnection bi1 the operator at thecentral `olice after the subscriber disconnects This condition issimulated by operating the automatic signaling .trunk key BIB to openthe v sleeve conductor 323. Busy lamp 3H is extinguished-one andone-half seconds after the operation of key 3I6. Relays 3S! and 3Urelease. Relay 3T operates to maintain guard lamp 30| lighted. Duringthe open sleeve interval before relay 3T is connected tov the sleeve,the trunk sleeve relay isgiven an Opportunity to release. It remainsreleased removing the condition which has kept the busy lamp 3|'Iylighted.

What is claimed is: Y Y

1. In a telegraph exchange system, a central oiiice, comprising anoperator switchboard, a test board, main trunks terminating at saidcentral oflice each havingv an appearance-at a position of saidswitchboard and a position of said test board, a testing trunk at saidtest board, having means for connection at said switchboard to any oneof said main trunks, and means at said test board for determining thecondition of any one of said main trunks, said means comprising patchingmeans for interconnecting at said test board said testing trunk and oneof said main trunks, signal devices connected to said patching means,and operable meansV arranged, when operated, to cause said signaldevices to indicate whether a selected trunk is busy, idle or in thecondition wherein a call from a distant point is awaiting'an answer,

2. In a telegraph-exchange system, a central If the subscriber disil i)oce comprising an operator switchboard, a test board, main trunksterminating at said central office each having a three-conductorappearance at a position of said switchboard and a position of said testboard, a three-conductor testing trunk at said test board and havingmeans for connection at said switchboard to any one of said main trunks,a trunk sleeve relay connected to one of said conductors at each of theappearances at said switchboard and arranged for connection to one ofthe conductors of said testing trunk, a high resistance operable elementconnected inparallel to said one conductor of said testing trunk, asignal device for holding a main trunk busy against subsequent seizureafter said testing trunk is connected to the particular main trunk, andoperable means arranged when operated to cause the operation of saidelement to operate said signal device and to prevent the operation ofthe sleeve relay in said particular main trunk. A

3. In a telegraph exchange system, a central oflice, comprising anoperator multiposition switchboard, a test board, main trunksterminating at said central loflice each having a threeconductorappearance at each position of said switchboard and a position of saidtest board, a three-conductor testing trunk at said test board andhaving means for connection at said switchboard to any one of said maintrunks, two-conductor means at said test board for indicating a callincoming over any one of said main trunks, said means comprisingtwo-conductor patching connector for associating at said test board theparticular main trunk with said testing trunk, and signalingelements-arranged to successively operate in response to the incomingcall, one of the conductors offsaid patching .connector being effectiveto operate one of said signaling elements at one time and another of theconductors of said patching connector being eiective to operate anotherof said signaling elements at another time. y

d. In a telegraph exchange system, a central office comprising anoperator multiposition switchboard, a test board, main trunksterminating at said central cnice, each having a three'- conductorappearance at each position of said switchboard and a position of saidtest board, a three-conductor testingl trunk at said test board havingmeans for connection at said lswitchboard to any one of said maintrunks, and twoconductor means at said test board for indicating a callincoming over any vone of said main trunks and said testing trunk,signaling means successively operative in response to an incoming callarranged to successively returnto normal when the call is abandonedbefore. the call is answered, and .means controlling one of saidsignaling elements arranged to vreoperate said one element after beingreturnedto normal, if the call is renewed within four. seconds.. 5. In atelegraph system for answering incoming calls at a test board, a centraloflice comprising an operator multiposition switchboard, a multipositionltest board, main trunksterminating at said central oiice, eachhavingran appearance at each position of said switchboard and a positionof said test board, a testingtrunk at said test board and having meansfor connection at said switchboard toanylone of said main trunks,patchingmeans at `vsaid test board ,for associating any one. ofV saidmain trunks with said testing trunk and sources of potential in saidmain trunk for energizing' said patching Ya call incoming Vmeans andAmeans.when:effectively associated with onecf ."tion betweensaidonemaintrunk vand said testsaid-main trunks at -said testingtrunk,signaling elements -at said-"test board, voperable meansin said Ytestingtrunk, a -teletypewriter -arranged-rior connection to said testingtrunk, means for energizing two said signaling velements'inrespcnse l-toover. one of said main trunks Awhen said one main trunkiseiectivelyrassociated `with said testing trunk` by saidfpatching means,`high resistance means responsive totthe yoperation of said operable`means for operating v.the third of'said signaling elementsand other-means effective to deenergize said-third-signaling vnaling means findependently of said-high `resistance means for the durationvofv theconnection established betweensaid teletypewriter and said -one maintrunk through said testing V'trunk in response to the incoming callswhen saidoperrablemeans is restoredto normal.

6.V In atelegraph exchange system for recall- -ing-the test boardattendant in acommunication connection, a centraloicecomprisingan-operator multiposition switchboard, a multipositiontestboard, main trunk vterminating -at said central ofice, yeach having.a three-conductor vappearance at each positionv of said switchboard anda position of `said test board, a three-conductor testing trunk at saidtest board and hav- :ing means for connection at said switchboardtcany-'one of said main trunks, an operable device Ain said testing trunkarranged to operate when aground potential is applied to one conductorof any one of said maintrunks .in engagement with said testing trunk,another operable device in said testing trunk arranged to operate .and

vlock in its'operatedpositon 'in response to the operation-of thefirst-mentioned operable device, a signaling element at said testboardarranged to operate intermittently during vthe time' that saidother operable device is locked in its `operated position, and 'an`operable Velement located at said test board and arranged whenv operatedmomentarily vto deenergize said operable` devices andsaidsignalingelement.

'Z-.`In a telegraph exchange system hfororigi: nating. aV call #at anattendants test boardvfor .a connection- `to a main trunk, a centraloffice comprising `an .operator multiposition switchboard,

-a multi-position test board,.rnain trunksl terminating at saidlcentraloffice, each-having asthreeconductor appearance-'at each position of:said switchboard and a position of said test -boarda testing tru'nk atsaid test vboard and yhaving means for connection at said switchboard toany -one'of saidmain trunks, patching meansatsaid testr Vboard forassociating any one fof rsaid .main trunks with said testing trunk andla source of potential in said main trunks for energizing said patchingAmeans, when effectively associated with one of said main trunks andsaid testing trunk, operable means at said'test board, signalingelements at said test board and said switchboard, means responsive -when(1) said patching means iseiectively associated with said one mainvtrunk and -said testing trunk, (2) said operable means is'` operated,and (3) said testing trunk is yconnectedto said onemain trunk, foroperating one oiA the signaling elements located at-said switchboard-andassociatedwith said one main trunk, and vmeans responsive vto therelease of said operable means for (1) making said one main trunk busyto other calls, (2) for maintaining operated the'said onesignalingelement v-at sa`id switchboard, '(3) 'for completingy an operativeconnec to maintain energized said third sigingztrunk, and (4)aforoperating a signalingele- `ment at: saidtestiboard to furnishsupervision-for /theldurationof the connection originated at the-attendants .test board.

`8. In a .telegraphsystem for sending call directing signals from anattendants test 4board to .any-.one of a plurality of main trunks, acentral cnice, comprising an operator multiposition switchboard, amultiposition test board, main sition :of `said switchboard and` onevposition fof -saicl test board, a three-iconductor testingtrunk atisaid.test boardv and arranged for connection atsaid? .switchboard to any oneof saidmain trunkswa teletypewriter connected. at said testy-lcoardl.to,.,saidy testing trunk Ikfor sending` call directing signalsoyerone of said conductors in said ,testing .trunk and one of saidconductors insaid main: trunk in engagement 'with said testing trunk, anoperable device at 'said test board, a high-resistance operable elementin lsaid'testing trunk and arranged tooperate in response to theoperationof-said operable device, a second and a third .operableelementin said testing trunk successively responsive tothe restorationto normal ofsaid operableidevice said-secondi operable element being,eifective when operated, to connect said teletypewriter ythrough saidtesting `trunk to said engagedmaintrunk for transmission of-ca11directing-signals. Y

..9...In av telegraph exchange systemv having a 4satellite communicationarrangement, afcentral oce,va `swift-ching center, a plurality ofsubvscrbersline's connected to said switching vcen-- ter, 'a pluralityoi main trunks interconnecting said vcenter and said central cnice,-said central ofice comprising an koperator Vmultiposi-tionswitchboardand-a multiposition test board-a .three-conductor appearancefor each of said main trunksat each position of said switchboard and one.position of said test board, a three-conductor testing trunkatfsaidtest board and varranged for connection at said switchboard toany oneof said main trunks, a teletypewriter connected at said.'testrboard to said Ytesting-trunk for sending-call directingsignalsfto said switching center, ancperable devicepl'ocated in said.testing trunk-and arranged to operate in `response to the initiation ofa call at said test board tosaid switchingcenvter andztofrelease inresponseA to the completion ofsaid call Vat said switchingcenter, asecond operable device Varrangedto operate and .lockinanoperatedpositionin response to the operationA of the first-mentionedoperable device, a signaling element-arranged to operate to onecondition -in response to the operation of the mst-*mentioned operableydevice and to another condition when the first-mentioned device isreleased during `the time that saidsecond operable device is initslocked position, said signalingv element in said other condition,furnishing an indication that-the switching center is ready` to receivecalldirecting signals for selecting the desired subscriber line'. t 10.In a telegraph exchange system having a satellitecommunicationarrangement, av central cnice, a switching center, a plurality ofsubscriber lines connected to vsaid switching center, a .plurality ofmain trunks interconnecting said center and said central oice, saidcentral oiiice'ccm#- prising an operator multiposition switchboard and amultiposition testboard-a three-conductor appearance ior each of saidmaintrunks atfeach A position of said switchboard and a positiongof saidtest board, a three-'conductor 4testing trunk'a't said test boardarranged for connection at said switchboard to any one ofsaid maintrunks, a teletypewriter removably connected at said test `board to4said testing trunk for sending call-di- ,trunk and arranged in responseto the operation of said operable device ,to a steady conditionuto-change from a varying .conditionto a steady condition to indicatetoatest board attendant that the"desired,subscriber line at rthe switchingcenter has been selected and connectedto said one main trunk inresponseA Ato the call directing .signals transmitted from rsaidteletypewriter.

y 11. In a telegraph exchange system having a satellite communicationarrangement, va central oflice, a switching center, a. plurality ofsubscriber lines connected to said switching center, a plurali-ty ofmain trunks interconnecting said cen.- ter at said central olice, saidcentral oliice com.- lprising an operator multiposition switchboard anda multiposition test board, a three-conductor appearance for each ofsaid main trunks ateach position of said switchboard and a position ofsaid test board, al three-conductor testing trunk at said test boardarranged for connection at said switchboard to any one of said maintrunks, a teletypewriter removably connected at said test board to saidtesting trunk for sending call directing signals to said switchingcenter, means responsive to the call directing signals ,from said.teletypewriter for automatically connecting said one of said maintrunks to one of said subscriber lines, a source of ringing current,switchingmeans in said testing trunk for applying ringing current fromsaid source to said automatically established connection of said onesubscriber line, and a signaling element at said test board arranged tooperate when the ringing current from said source is applied to theautomatically established connection.

Y 12. In a telegraph exchange system having a satellite communicationarrangement, a central olflce, a switchin-g center, a plurality of,subscriber lines connected to said switching center, a plu.- D

rality of main trunks interconnecting said center at said central oilce,said central oflce comprising an operator multiposition switchboard anda multiposition test board, a three-conductor appearance for each ofsaid main trunks at each position of said switchboard and a position ofsaid test board, la three-conductor testing Ytrunk at said test boardarranged for connection at said switchboard to any one of said maintrunks, a teletypewriter removably connected at said test board to saidtesting trunk for sending call directing signals to said switchingcenter, to select a desired subscriber line, an operable device locatedat said testing trunk and arranged in response to a connection beingautomatically established between one of said main trunks and one ofsaid plurality of subscriber lines by said call directing signals, tooperate to a steady condition, a second operable device arranged tooperate and lock in an operated position in response to the operation ofthe first-mentioned operable device, an indicating signal and a sourceof alternating current arranged to be connected to said indicatingsignal when said second operable device .Operates whereby a flashingsignal is furnished to invdicate that s aidiautomatically, establishedconnection is in a condition vfor telegraphic message communication, anda switching memberfor restoring said second operable device to normal.

13. In a telegraph exchange system according to claim 10, wherein eachofsaid main trunks comprises a sleeve relay normally operated when itsassociated trunk is in a busy condition, interconnected make-busy jacks,an answer lamp signal, vandmeans for maintaining the trunk busy during abusy condition when the sleeve relay is given an opportunity to release,'and said testing trunk comprises switching means, a plurality ofrelays,one relay of said plurality having a vrelativelyhigh'resistancegvalue and certain other relays of said plurality beingnormally operated during an established connection between said testingtrunk and any one of said main trunks, means cooperating with.- one ofsaid certain relays for normally maintaining the sleeve relay of saidone trunkA operated during the established connection between `said,testing trunk and said one main trunk, circuit means responsive totheoperation of said switching means for releasing said certain re,- layssuccessively, other circuit means responsive to the release of saidcertain relays for operating said relay of relatively high resistancevaluey and a sleeve conductor circuit in said testing trunk and said onemain trunk connected thereto effective during its open conditioninterval created between the time of the operation` of said switchingmeans and the `complete release of the last 'operated of said certainrelays, to operate said relay of relatively high resistance value and toafford theopportunity to release to said trunk sleeve relay, said busymeans of said one trunk including relays cooperating with said make-busyjacks in busy condition to operate said answer lamp signal;

14. In a telegraphexchange system according to .claim 10, wherein eachof said main trunks comprises a make-busy jack, an answer lamp signal, abusy lamp signal, and means for maintaining theA trunk busy when saidtrunk is in a busy condition, and said testing trunk comprisesswitchingmeans, a plurality of relays, one relay of said plurality having arelatively high resistance value, and'certain other relays of saidplurality being normallysfoperated during an establishedconnectionbetween said testing trunk and any one of said main trunks,means cooperatingwith one of said certain relays for maintaining thesleeve relay of said one trunk operated during the esta' lishedconnection between said testing trunk and said one main trunk, circuitmeans responsive to the operation of said switching means for releasingsaid certain relays successively, other circuit means responsive to therelease of said certain relays for operating said relay of relativelyhigh resistance value, and sleeve conductor means in said testing trunkand said one main trunk connected thereto eiective during the opencondition interval created between the time of the operation of saidswitching means and the complete release of the last operated of saidcertain relays to operate said relay of high resistance value and torelease said vtrunk sleeve relay, and means in said one main trunkcooperating with said make-busy jack in `busy condition, said busy meansof said one trunk including relays cooperating with said make-busy jackin busy condition to operate said answer and said busy lamp signals, andrestoring means responsive to the opening of the estabe lishedconnection at the subscriber line end for releasing, first, said answerlamp andthen, after a predetermined interval, said busy lamp.

15. I'n a telegraph exchange system according to claim 10, wherein saidone of said main trunks comprises means for connecting ground potentialto one of the conductor circuits of said testing trunk when saidestablished connection is opened at the subscriber line end of theestablished connection, to reoperate, in turn, said operable device andsaid signaling element whereby the hashing condition of said signalingelement is changed to a steady condition to indicate that thetelegraphie message communication is concluded, and means responsive tothe removal of said testing trunk from one said main trunk for restoringthe testing trunk and said one main trunk to normal.

16. In a telegraph exchange system according to claim 10, wherein eachof said main trunks comprises a sleeve relay normally operated when itsassociated trunk is in a busy condition, interconnected make-busy jacks,an answer lamp and a busy lamp signal controlled by said make-busy jackswhen in busy condition, and means for maintaining the trunk busy duringthe busy condition when the sleeve relay is given an opportunity torelease, and said testing trunk comprises switching means, a pluralityof relays, one relay of said plurality having a relatively highresistance value, and certain other relays of said plurality beingnormally operated during an established connection between said testingtrunk and any one of said main trunks, means cooperating with one ofsaid certain relays for normally maintaining the associated sleeve relayof said one trunk operated during the estblished connection between saidtesting trunk and said one main trunk, circuit means responsive to theoperation of said switching means for releasing said certain relayssuccessively, other circuit means responsive to the release of saidcertain relays for operating said relay of high resistance value, asleeve conductor circuit in said testing trunk and said one main trunkconnected thereto effective during its open condition interval createdbetween the time of operation of said switching means and the completerelease of the last operated of said certain relays to operate said highresistance relay and to give an opportunity to release to saidassociated sleeve relay, a guard signaling element responsive to theoperation of said high resistance relay, and circuit means in said onetrunk responsive to the operation of said switching means for releasingsaid busy lamp signal said release being effected after a predeterminedinterval that said switching means remains in an operated position.

TOLA A. MARSHALL.

